California Air Resources Board

CARB should allow the use of the following assurance frameworks for Scope 1 and Scope 2 emissions reporting for the first reporting year (FY 2025, reported in 2026): International Auditing and Assurance Standards Board’s (IAASB) International Standard on Assurance Engagements (ISAE) 3000, Assurance Engagements Other Than Audits or Reviews of Historical Financial Information (Revised), ISAE 3410, Assurance Engagements on Greenhouse Gas Statements OR any country / jurisdictional equivalent of international standard ISSA 5000 (ex. ASSA 5000 – the Australian Auditing and Assurance Standards Board (AUASB) Standard on Sustainability Assurance General Requirements for Sustainability Assurance Engagements).

The IAASB’s International Standards on Sustainability Assurance (ISAA) 5000, General Requirements for Sustainability Assurance Engagements, which will replace ISAE 3000 and ISAE 3410, is effective for assurance engagements on sustainability information reported for periods beginning on or after December 15, 2026. IAASB will withdraw ISAE 3410 upon the effective date of ISAA 5000 (December 15, 2026). ISAE 3000 will continue for assurance on other types of information that is not sustainability information.

Companies that already obtain external assurance over their greenhouse gas emissions are likely to have been using IAASB’s previously available standards (ISAE 3000 and ISAE 3410). These companies will also likely continue to utilize these standards until the effective date of ISAA 5000, if not otherwise required by jurisdictions or regulators who choose to adopt and apply it earlier. Since SB 253 will impose a June 30, 2026 implementation deadline for reporting on the prior reporting year’s Scope 1 and Scope 2 emissions (FY 2025), the use of ISSA 5000 will not yet be required, and ISAE 3000 and ISAE 3410 will still be available for use. Additionally, ISSA 5000 has 212 requirements, which is more than double those of ISAE 3000. This adds a significant increase to the amount of work required for both the reporting company and assurance provider. The effective date of ISSA 5000 was intended to leave preparers and assurance providers with sufficient time to prepare for the impact.

For these reasons, CARB should allow companies to utilize ISAE 3000 and ISAE 3410, OR any country / jurisdictional equivalent of international standard ISSA 5000 for the first reporting year, to align with the timeline of ISAA 5000’s effective date.